The prior art related to the field of dental implants includes various examples of dental implants and insertion tools.
A typical dental implant according to the prior art includes an external thread which is driven into the bone and an internal thread which accepts an insertion tool. In the past, the insertion tool was screwed into the implant, the implant was screwed into the bone, the insertion tool was unscrewed from the implant and discarded. This process is inherently time consuming and, therefore, disadvantageous.
Another disadvantage of this type of conventional dental insert is related to the process of unscrewing the dental implant from the insertion tool after the implant has been inserted into the bone. The process of unscrewing the insert is disadvantageous because the process inherently tends to loosen the contact between the insert and the bone.
Another example of prior art dental inserts is shown in U.S. Pat. No. 4,960,381 issued to Gerald A. Niznick for a Screw-Type Dental Implant Anchor. The Niznick patent shows a screw-type dental implant anchor which includes an externally threaded body portion which includes an internal structure for engaging an insertion tool. The top portion of the implant anchor is open and in registry with an internally-threaded portion. The top portion of the anchor forms a head portion which includes a hex-shaped cavity in its inner wall surfaces for receiving a hex wrench. The internal hex-shaped configuration is intended to allow the insertion of the anchor in the jawbone of a patient using an Allen-type wrench.
One of the significant disadvantages of the Niznick device is related to the arrangement of the hex-shaped cavity which is positioned directly above the internally threaded portion. As shown and described in the Niznick patent, the smaller distance across the hex-shaped cavity is greater than the external diameter of the internal threads. This configuration creates stress concentrations which results in high stress lines along the hex corners. This problem has resulted in numerous implant fractures.
Another example of prior art dental inserts is shown in U.S. Pat. No. 6,464,500 to Don D. Popovic for a Dental Implant and Abutment System. The Popovic patent showed a screw-type dental implant anchor which includes an externally threaded body portion which includes an internal structure for engaging an insertion tool. The top portion of the implant anchor includes an internally threaded portion. A hex-shaped cavity is located below the internally threaded portion for the purpose of receiving a hex wrench. As in the Niznick patent previously described, the hex-shaped cavity is intended to facilitate the insertion of the anchor in the jawbone of a patient using an Allen-type wrench. As a result of the location of the hex-shaped cavity below the internally threaded portion, the distance between corners of the hex-shaped cavity is smaller than the internally threaded portion.
The hex-shaped cavity is therefore so small that at normal insertion torques, there is the distinct possibility of damage to the insertion tool and damage to the insert. This is especially true in the event that the insert binds prematurely in hard bone. This is caused by the required relationship between the internal threads and the hex-shaped cavity. The largest thread normally used has a diameter of about 1.5 millimeters, mm. The distance between the corners of the hex has to be smaller than 1.5 mm, otherwise the insertion tool would not clear the internal threads.
As a result, neither the configuration of the Niznick device with the hex-shaped cavity above the internally threaded portion nor the Popovic configuration with the hex-shaped cavity below the internally threaded portion provides a satisfactory dental implant.
Another example of a prior art dental implant is shown in U.S. Design Pat. No. D446,859 issued to Steven M. Hurson for a Multi-Lobed Dental Implant. The Hurson patent shows a screw-type dental implant which includes an externally threaded body portion and an internal cavity for engaging an insertion tool. The Hurson device is generally similar to the Niznick device and the top portion of the implant is open and in registry with an internally threaded portion. The top portion of the implant includes a multi-lobed cavity. In a manner similar to the Niznick device, the multi-lobed cavity extends beyond the external or maximum diameter of the internal threads. As explained in connection with the Niznick device, this configuration creates stress-concentrations where there are discontinuities in the cross-section, such as at the corners of the lobes. As explained previously, these stress concentrations can lead to loss of structural integrity of the implant. These problems are increased when there is an attempt to manufacture the Hurson or the Niznick devices in the relatively narrow configurations which are required for narrow edentulous areas.
An example of the problems associated with prior art implants is described in an article titled “Ridge Augmentation for Immediate Postextractive Implants: Eight Year Retrospective Study” by A. Ashman, DDS, J. Lo Pinto, DDS, and J. Rosenlicht, DMD, in Practical Periodontics and Aesthetic Dentistry, Vol. 7, No. 2, March 1995, page 89. The article shows an insert with a hex-shaped cavity cut in the internal thread, in which the internal thread was stripped by the insertion tool during surgical placement. This problem resulted in a need to cut a new thread into the implant.
Despite the developments of the prior art, there remains a need for a dental implant which can be installed in a safe and reliable manner.